474 SYDNEY J. HICKSON. 



The collection made by Mr Gardiner in the Maldives affords an opportunity of judging 

 of the extent of variation possible in one group of islands of some other genera that are 

 widely distributed. 



In the case of the genera Spongodes and Solenocaidon, for example, it is clear that 

 there is a very great range of variation in form, colour, and in the size and shape of 

 the spicules. They exhibit a number of " facies " which form an almost uninterrupted 

 series between the types that have been described as distinct species. Now these facies 

 are not confined to any one island of the Maldive archipelago, nor are they clearly 

 separated from similar facies found in other parts of the tropical Indian and Pacific 

 Oceans. If each facies represents a distinct species, then we have the very remarkable 

 phenomenon of a large number of closely related species distributed over a very wide 

 geographical area and competing in the struggle for existence, with approximately equal 

 success, in many localities of this wide area. If, on the other hand, all the facies together 

 represent but one species, then we have an example of a species that is capable of an 

 extraordinary range of variation in circumstances which are approximately identical. 



As it is impossible to prove either one of these propositions without recourse to 

 experiments in cross breeding, the only course to pursue, as a temporary measure, is to 

 place in a separate species those facies which appear to be discontinuous with others in 

 their form and distribution, and to collect into one species those facies that are connected 

 by sufficiently continuous series of intermediate links. 



This is the course I have adopted in this paper. 



As an example of the method I may refer to the genus Solenocaidon, in which we have 

 no less than eight specimens from different islands of the Maldive archipelago connected 

 together to form a series, and one specimen which I have called S. ramosa distinguished from 

 them in the tube-formation of the stem, the retractility of the polyps and other characters. 

 This last I regard as a distinct species at present, but I think it is quite possible that 

 a series of intermediate forms between it and S. tortiiosum may be found which will ultimately 

 necessitate the abandonment of the specific name. 



It is a question of very great importance as bearing upon the species problem, whether 

 the varying forms and colours of these Alcyonarians are due to sporadic variation irrespective 

 of their environment or to distinct inherited characters. 



If we were to trace the history of 20 eggs of a brown divaricate Spongodes fertilised 

 by the spermatozoa of another brown divaricate Spongodes, and settled down within a 

 restricted area of a single reef, should we expect to find that all the young Spongodes 

 developed from them were brown divaricates (BD), or should we expect to find that .some 

 of them were red conglomerates (RC), others yellow flabellates (YF), etc.? If they are all 

 BD, with of course variations in minor particulars, then we should be justified in believing 

 that the brown colour and the divaricate manner of branching are not only transmissible 

 by inheritance, but are so transmitted because they are of some importance to the species 

 in the struggle for existence. If on the other hand the young Spongodes are of the facies 

 BD, RC, YF, etc., then we should be justified in believing that the characters of the colour 

 and mode of branching are of little or no importance for the species in the struggle for 

 existence, but are due to the direct action of the environment (e.g. sunlight, food supply, 

 strength of currents, proximity of neighbouring zoophytes, presence of epizoic Crustacea, etc.). 



